The present invention relates to method for adjustment of hammer let off on a keyboard musical instrument, and more particularly relates to method for minimizing the hammer let off distance on a keyboard musical instrument provided with a plurality of action assemblies each including a swingable catcher and a hammer adapted for striking an associated string, and a mute assembly including a stopper adapted for prohibiting continued swing of said catchers just before string striking by the hammers.
Various type of pianos have recently been developed in the field of keyboard musical instruments, which are provided with silent systems in addition to the conventional muffler systems. A muffler system is used for buff citing string sounds once generated by string striking whereas a silent system is used for prohibiting generation of string sounds themselves. More specifically in the case of a silent system, each action assembly is driven for operation in response to key operation. However, continued swing of a hammer in the action assembly is prohibited just before striking an associated string. In a typical arrangement of such a silent system, a silent assembly includes a stopper which intercepts continue swing of a catcher related in action to an associated hammer via a butt of a hammer assembly. Such a silent system is disclosed in Japanese Patent Application Hei. 4-174807 filed in 1992 by the applicant of the present invention. Use of such silent system allows normal performance and silent performance on keyboard musical instruments. Even during silent performance, musical sounds can be generated in electronic fashion for the convenience of players though no string sounds are generated in a mechanical fashion.
Silent system, however, is inevitably accompanied with degradation in key touch feel. In order to prohibit generation of string sound, the above-described stopper in the silent assembly needs to be moved towards a hammer shank in the hammer assembly. Here, a term "let off distance D" refers to the distance between a hammer and an associated string at a moment when the hammer gets out of operation by a jack and starts to swing freely. In the case of an conventional piano, the value of the let off distance D is 3 mm for the bass range, 2.5 mm for the middle range and 2 mm for the treble range.
When the let off distance for silent performance is set to a value equal to that on the conventional piano, the butt of the hammer assembly is clamped between a jack and a stopper of tile silent assembly before disengagement of the jack from the butt. As a result, piano performance such as tremolo performance cannot be carried out. In order to avoid such a trouble, it is necessary to reduce the distance between the jack tail of the hammer assembly and a regulating button on a center rail in order to allow earlier disengagement of the jack from the butt. This adjustment inevitably causes increased let off distance D. For example, the let off distance D is increased up to 10 mm or larger. Such a significant increase in let off distance causes corresponding change in key touch feel. In addition, advanced disengagement of the jack reduces energy to be supplied from the jack to the butt and, as a consequence, reduces striking power of the hammer during normal performance, thereby causing generation of music sounds of softer tone colours than normal.
Variation in height of catchers, i.e., positional variation of catchers relating to variation in angle between catchers and hammers or shanks wields a great, malign influence on silent performance. In the case of general pianos, the variation in height of catchers is in a range of .+-.1 mm and a variation of this extent has no substantial malign influence on normal performance. That is, the variation can be disregarded in the case of normal performance by using a mute system with a catcher stopper. The variation of this extent, however, wields a great influence on key touch in the case of silent performance. The ratio in swing movement of a catcher with respect to an associated hammer is generally in a range from 2 to 3. So, when swing movement of a catcher is prohibited by a stopper just before a hammer strikes an associated string, variation in height of the catcher is amplified by 2 to 3 times on the side of the hammer. For example, when variation in height of the catcher is in a range of .+-.1 mm, resultant variation in position of the hammer is in a range of .+-.3 mm. Let off position of the hammer must be determined based on the largest value of the positional variation of the hammer when the hammer swing is prohibite.
In consideration of such a background, the let off distance is usually set to a value somewhat larger than the largest value on a keyboard musical instrument incorporating a conventional silent assembly. As a result, the let off distance D with the conventional silent assembly is designed inavoidably too large to assure comfortable key touch feel.
In an attempt to avoid such a design, it is proposed to mount a stopper to a supporter via screw engagement so that the position of the stopper relative to an associated catcher can be adjusted by screw turning. In this way, the let off distance D of a hammer for silent performance can be made very close to that for normal performance in order to minimize degradation in key touch feel. This solution, however, necessitates delicate stopper position adjustment for all keys on the keyboard and, as a consequence, entails much time and labour. In addition, inevitable generation of vibrations during performance tends to disturb screw adjustment and, as a consequence, reproduces variation in stopper height.